X-ray apparatus



Nov. 29, 1960 P. A. DUFFY, JR

X-RAY APPARATUS 3 Sheets-Sheet 1 Filed Sept. 14, 1956 E 6 22. 21 .B Emo.: coo mm 2.5.750

mmuto 31 x EEE INVENTOR Philip A Duffy, Jr. Y5 W ATTORNEY B m 3 m 3.50mmuuro 350 053 23 WITN ESSES Nov. 29, 1960 P. A. DUFFY, JR 2,962,594

X-RAY APPARATUS Filed Sept. 14, 1956 s Sheets-Sheet 2 93 BrightnessSignal 920 Pre-Amplifier Contocior 65 63 63 Start-810p Cumeru Control $4Motor Circuit 1 f 12 J F192. 20

1950 P. A. DUFFY, JR 2,962,594

X-RAY APPARATUS Filed Sept. 14, 1956 3 Sheets-Sheet 3 F e H I I I I I II I II II I I I I I I I I g I l I I I I I I I I I I I I I I I Fig.4.

Fig.5.

United States Patent X-RAY APPARATUS Philip A. Duffy, Jr., Catonsville,Md., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Filed Sept. 14, 1956, Ser. No.609,900

16 Claims. (Cl. 250-95) The present invention relates to improved X-rayapparatus and more particularly to an improved control to maintainsubstantially constant brightness of the resultant X-ray picture.

In X-ray apparatus including a fluorescent screen for providing avisible image, there is a problem of maintaining the brightness of thevisible image substantially constant as different thicknesses of objectsare subjected to the X-rays or when objects having varying X-ray opacityare scanned by the X-ray beam. The same problem also arises when theX-ray apparatus is used in the process of making motion pictures of thefluorescent image and Where the area of the object subjected to theX-ray beam is changed to a different area having a new thickness orwhere material having a different opacity is moved into the field of theX-rays during the exposure of successive frames of motion picture film.Even when every effort is made to accurately predict the X-ray tubevoltage and current requirements prior to initiation of photographicsequence, it has been found that a given strip of motion picture filmwill vary from under-exposed frames to over-exposed frames in the courseof a single sequence.

In the first experimental efforts to solve the foregoing problemapparatus was employed in which a phototube responsive to the imagebrightness was connected to circuitry for varying the X-ray tubefilament voltage supply so as to control the X-ray tube milliamperage ininverse proportion to the image brightness. While that experimentalsystem rendered a considerable improvement in brightness stability, itwas found that substantial constancy of image brightness during a normalfluoroscopic medical examination would require variation of the X-raytube current over a range of 100 to 1. Such a wide variation of X-raytube current is prohibited by the capacity limitations of practicalX-ray generators and is further precluded by biological radiation safetyrequirements.

An X-ray tube requires a high voltage for its operation. Oneconventional source of high voltage is a circuit comprising a hightension transformer and a plurality of rectifier devices. The lowvoltage primary of the transformer is ordinarily connected to acommercial voltage source, and the high tension secondary winding of thetransformer is connected through a bridge rectifier circuit to thecathode and anode of the X-ray tube.

Accordingly, it is an object of the present invention to provide animproved control for the X-ray tube voltage or power source.

It is another object of the present invention to provide improved X-rayapparatus including a brightness stabilizing circuit responsive to theintensity of the visible fluorescent image.

It is a further object of the present invention to provide an apparatusfor continuously controlling the intensity a an X-ray beam.

It is an additional object to provide a brightness stabilizing circuitfor an X-ray apparatus having a power source including a high tensiontransformer with an associated rectifier circuit for supplyingunidirectional current to an X-ray tube.

It is a different object to provide a brightness stabilizing system forX-ray apparatus which includes two separate and cooperative means forvarying the intensity of the X-ray beam with one of said means beingoperative to control the voltage applied to the X-ray tube and with theother of said means being operative to control the anode currentconducted by the X-ray tube.

It is a still further object to provide an X-ray apparatus utilizing anelectronic contactor controlled by an image brightness responsive meanswhich is capable of producing X-ray exposures having a time duration ofless than of a second.

It is still another object to provide an X-ray apparatus utilizing anelectric contactor controlled by a'photosensitive device to variablycontrol the voltage applied to the X-ray tube in inverse response to theintensity of an X-ray beam penetrating an object.

These and other objects and advantages of the. invention will beapparent during the course of the following description. The invention,however, both as to its organization and method of operation will bebest understood from the following description when read in connectionwith the accompanying drawings in which:

Figure 1 is an illustrative block diagram of apparatus in accordancewith the present invention;

Fig. 2 is a detailed schematic diagram of significan portions of theapparatus in accordance with the present invention;

Figs. 3 and 4 are wave-shape diagrams illustrating the manner in whichvoltage is applied to the X-ray tube power supply circuit, and

Figs. 5 and 6 are vector diagrams illustrating the operation of aportion of the control circuit in accordance with the present invention.

Referring now to Fig. 1, there is shown an X-ray generator comprising anX-ray tube 10, a high voltage rectifier circuit 29 and an alternatingcurrent voltage source 19. The voltage source may be an autotransformer7 having a plurality of output terminals and having its input terminalsconnected through a circuit breaker20 to a suitable commercial source ofalternating current power 23, as shown in Fig. 2. Serially connectedbetween the alternating current voltage source 19 and the high voltagerectifier circuit 29 is an electronic contactor 101 which may comprise apair of inverse parallel connected thyratron tubes.

Adjacent the X-ray tube 10 is positioned an object support member 17 forsupporting a patient or object 57 in a position for projecting a beam ofradiation through the object from the X-ray tube 10. As in the usualarrangement the X-ray tube 10 may be movably mounted to traverse a planeof considerable area adjacent to the support surface 17. Adjacent thesupport surface 17 on the opposite side thereof from the X-ray tube islocated an image intensifier device 43 having a fluorescent imageformingscreen 47. The image intensifier tube 43 is shown diagrammatically andcomprises essentially a preferably cylindrical container having at oneend an X-ray sensitive and photoelectric emissive screen 44. An electronimage created by the photoelectric screen 44 is projected to an electronsensitive fluorescent screen member 47 where it produces a visible imageof reduced dimensions and increased brightness corresponding to theX-ray image projected on the X-ray sensitive screen 44. An image intensifier of a type which may be used in. the present apparatus isdescribed in detail in Mason et a1. Patent 2,523,132.

An optical focusing means 40 contained within a housing 41 is positionedadjacent the image intensifier tube 43 and operates to focus an imagefrom the fluorescent film transport mechanism are a plurality ofcommutator type switch devices 63 each having an angular conductiveportion 67, Fig. 2, and a cooperative brush 65 to provide cyclicalvoltage pulses in synchronism with the position- -ing of successive filmframes at the focal plane of the camera 60. The voltage pulses providedby the commutator switch 63 are transmitted to an electronic contactor101 and are there operative to control conductivity of the contactor,such that the contactor 101 will energize the X-ray generator onlyduring successive intervals when the film in the motion picture camera60 is properly positioned for exposure.

A light responsive member or photosensitive means 49 I is positionedrelative to the fluorescent screen member 47 so as to intercept aportion of the visible light emanating from the screen 47 and isoperative to produce an electrical signal responsive to the brightnessof the visible image on the fluorescent screen member. The lightresponsive member 49 may be a photosensitive electron tube of thephotomultiplier type, such as the RCA type 931A. The photomultipliertube 49 is provided with energizing voltage by conventional power supply51 of the type normally used with such tubes. The light responsivemember 49 is connected to a brightness signal preamplifier circuit 53which will be discussed in further detail hereafter. A first outputsignal 55 of the brightness preamplifier circuit 53 is connected to anX-ray tube voltage control brightness stabilizer circuit 71, which is inturn connected to the electronic contactor 101 so as to control theaverage conductivity of the electronic contactor. More specifically, thevoltage control brightness stabilizer circuit 71 is responsive to asignal proportional to the brightness of the light image at thefluorescent screen member and operates to impose a control voltagecomponent on the electronic contactor 101, so as to control the periodof cyclical conductivity of the contactor 101, thereby controlling thevoltage applied to the X-ray tube in inverse response to the brightnessof the fluorescent light image at the fluorescent screen member 47.

A second output signal 54 of the brightness preamplifier circuit 53 isconnected to an X-ray tube current control brightness stabilizer circuit132. The current control brightness stabilizer circuit 132 may be acircuit similar to that shownby Weisglass Patent 2,319.378, or may beother known power amplifier circuits which are adapted to control thecurrent .in an AC. circuit in inverse response to variations in a DC.signal voltage 54 applied as from the brightness signal preamplifiercircuit 53. The current control brightness stabilizer circuit 132 isserially connected between a filament current supply source 15, Fig. 2,and the filament energizing circuit for the X-ray tube 10. By variationof an impedance 143 connected in series with the filament supply circuitthe electron emission of the X-ray tube filament 12 is controlled ininverse relation to the brightness of the image appearing at thefluorescent screen member 47, thereby controlling the current conductedby the X ray tube 10 in inverse relation to the brightness of thevisible image.

Referring now in detail to Fig. 2, the X-ray tube 10 including an anode11 and a filament 12 is connected through a full-wave voltage rectifyingcircuit 29, comprising a plurality of high voltage rectifiers 27, to thesecondary winding of a high tension transformer 31. The high tensionsecondary Winding comprises two winding sections 35 which are connectedin series through a milliampere meter 39 or a metering circuit of awellknown type. The end of one of the secondary winding sections whichis connected to the milliampere meter may be and is preferably grounded.The secondary windings 35 of the high tension transformer 31 areconnected to the full-wave rectifier circuit in series additiverelation, such that the voltage applied to the rectifiers issubstantially the sum of the voltages of the two secondary windingsections.

The primary winding 33 of the high tension transformer 31 has oneterminal connected, through conductor 36, directly to a suitableterminal on the power supply autotransformer 7. The other end of thehigh tension transformer primary is connected through the electroniccontactor 101 to an adjustable tap 9 on the power supply autotransformer7. Further included in the X-ray generator high tension circuit 29 is anV-ray tube filament energizing isolation transformer 37, which has itssecondary winding at a high DC. voltage level corresponding to thedirect current voltage impressed upon the filament 12 of the X-ray tube10, and which has its primary winding near ground potential with one endof the primary winding being connected directly to the common terminal 8of the voltage supply autotransformer 7 by means of the common conductor36. The other end of the X-ray tube filament transformer primary isconnected through the AC. windings 147 of a saturable reactor 143 in thecurrent control brightness stabilizer circuit 132, and thence to asuitable terminal of the voltage supply autotransformer 15.

The light responsive member 49 shown diagrammatically in Fig. 2 isphysically positioned, as shown in Fig. l, in optical relation to thefluorescent screen member 47 so as to be responsive to the brightness ofthe visible light image appearing on the fluorescent screen member 47and is operative to produce a direct current signal proportional to thebrightness of the visible image. The direct current signal from thephotoelectric light responsive means 49 is fed to the input of thebrightness signal preamplifier 53.

The brightness signal preamplifier circuit 53 is not shown in detail andmay comprise any of a large number of well-known DC. voltage amplifiershaving a high input impedance and having a low output impedance andbeing operative to produce a DC voltage proportional to the amplitude ofa DC current fed into the input. The only essential criteria for a DC.amplifier for use in the present apparatus is that it be reasonablystable and free from drift in its output voltage when the input currentis zero, and free from drift in amplification factor.

The brightness signal preamplifier 53 is provided with two similaroutput circuits 54 and 55, with one output circuit 55 being connectedacross the grid-cathode circuit of a discharge device 73 in the X-raytube voltage control stabilizer 71, and with the other output circuit 54being connected across the grid-cathode circuit of a discharge device137 in the current control brightness stabilizer circuit 132.

The current control brightness stabilizer circuit 132, which is providedwith an input signal from the brightness preamplifier 53 and which isoperative to control the voltage applied to the primary winding of theX-ray tube filament heating transformer 37, comprises a electrondischarge device 137, preferably of the vacuum type type, having ananode 141, a control electrode or grid 139, and a cathode 140. Thecurrent control brightness stabilizer circuit 132 further includes asaturable reactor 143 having a direct current control winding 145 whichis connected in series with the anode circuit of the power amplifierdischarge device 137 and in series with a suitable direct currentvoltage source 144, shown schematically as a battery, but which may beany conventional type of direct current power source. The saturablereactor 143 includes a pair of alternating current windings 147 whichare connected in parallel and in voltage opposing relationship withrespect to winding 145 and the parallel combination is connected inseries with the X-ray tube filament heating circuit comprising voltagesource 15 and the primary winding of transformer 37. The input signal tothe current control brightness stabilizer circuit 132 from thebrightness signal preamplifier 53 is connected across a grid resistor148 and is connected to the grid 139 of the power amplifier dis chargedevice 137. The cathode 140 of the discharge device 137 is connectedthrough a cathode biasing resistor 149 to the common side of thebrightness signal preamplifier output circuit 54 and to the negativeside of the direct current voltage source 144.

As the DC. output voltage 54 from the brightness signal preamplifier 53increases in response to an incremental increase in intensity of thevisible image at the fluorescent screen member 47, the control electrode139 of the power amplifier discharge device 137 is driven more negativewith respect to the cathode 140, thereby inducing a decreased currentflow to the anode 141, and through the DC. winding 145 of the saturablereactor member 143. The imposition of that negative component of directcurrent upon the DC. control winding 145 of the saturable reactoroperates to decrease the saturation of the magnetic core of thesaturable reactor 143, thereby increasing the impedance of thealternating current windings 147. The increased impedance in the AC.windings causes an accompanying increase in the voltage drop across thealternating current windings 147, thereby applying a reduced alternatingcurrent voltage to the primary winding of the filament heatingtransformer 37. The reduced voltage thus applied to the X-ray tubefilament 12 induces a decrease in electron emission from the X-ray tubefilament 12 so as to result in a reduced anode current through the X-raytube and the high voltage rectifier circuit. Thus, an incrementalincrease in brightness results in an accompanying decrease in X-rayintensity. It is to be noted that X-ray tubes conventionally operate atfilament saturation so that the anode current is a function principallyof the filament excitation as well as being secondarily a function ofthe voltage applied between the cathode and the anode.

During the course of a fluoroscopic examination the diagnosticianfrequently observes some organic function or malfunction in the anatomyof the patient of which it is desirable to provide a permanentphotographic record to substantiate the fleeting fluoroscopicobservation. For example, a suspected ulcer in the duodenal portion ofthe small intestine is often times observed for only a fleeting intervalduring the examination. Likewise, it is frequently desirable to providea strip of motion picture film recording the different phases of thepatients heart action. To be successful, apparatus for providing such aphotographic record must be instantly operable and available withoutdistracting the fluoroscopist from the image being examined.

In the apparatus of the present invention, the photographic recordingmeans comprises a motion picture camera 59 contained within a housing60, the driving motor 61 for the camera film transport mechanism, amotor synchronizing circuit 62 for insuring that the motor 61 issynchronized in phase with the voltage pulses applied to the X-ray tube10, a manual switch member 46 on the optical device housing 41, andrelay means connected between the said switch member 46, the motorsynchronizing circuit 62 and the electronic contactor 101.

In order to initiate motion picture photography, the operator moves themanual control member 46 on the optical device housing 41 from theuppermost position, as shown in Fig. 1, to the lowermost position, asshown in dotted lines in Fig. 1. Actuation of the control member 46operates suitable switches (not shown) within the optical device housing41 to energize suitable relays so 6 as to initially energize the cameradriving motor 61. As shown in Fig. 2, the camera motor 61 has connectedthereto a plurality of commutators 63, each of which is of insulatingmaterial and has an angular conductive segment 67 on its periphery. Oneof the said commutator switches 63 together with a brush 65 in contactwith the commutator and together with the contactor start-stop controlcircuit 87 comprises a first contactor control circuit for controllingthe conductivity of the electronic contactor 101. As the camera motor 61operates, the commutator 63 rotates to periodically complete a circuitfrom the contactor start-stop control circuit 87 through the brush 65and the conductive segment 67 to ground. As seen in Fig. 2, it may beconsidered that the rotating commutator 63 provides periodic pulses tothe contactor start-stop control circuit 87 in synchronism with thepositioning of successive film frames at the focal plane of the camera59'. The said periodic pulses are operative to cause the contactorcontrol circuit 87 to apply an alternating current voltage to theprimary of a control transformer 91. The details of the contactorcontrol circuit 87 are not shown in the present application in thatarrangements for the control of inverse parallel thyratron co-ntactorsare known in the art. A start-stop control circuit of a type suitablefor use in the present apparatus is shown by US. Patent 2,785,343, of R.L. Wright et al., issued March 12, 1957, for X-Ray Apparatus, andassigned to the assignee of the present invention. Such a contactorstart-stop control circuit 37 is operable to apply an alternatingcurrent voltage to the primary winding of the contactor starttransformer 91 during the time periods in which a control circuit isclosed through the rotating commutator 63. The start-stop controlcircuit is further operative to insure the application of voltage to thecontactor start transformer 91 at the beginning of the next succeedinghalf cycle of the alternating current supply voltage. The contactorstart control circuit 87 is necessary in order to assure that voltagewill not be applied to the contactor start transformer 91 at the peak ofa half cycle of the A.C. supply voltage, but will. be initiallyenergized only at the beginning of the first half cycle of appliedvoltage after the closing of the commutator switch 63, regardless ofwhen the commutator switch 63 is first closed with reference to thesupply voltage wave. The electronic contactor 101, shown in blockdiagram form in Fig. l, is shown in detail in Fig. 2 as comprising apair of inverse parallel connected discharge devices 1113 and 111, eachhaving an anode, a cathode, and a control electrode, and furthercomprising a filament heating transformer 119, 121 for each of thethyratron discharge devices 103 and 111 and a bias voltage supply 123,125. A grid con trol transformer winding 99, 1% and a grid resistor 127,129 are connected in series between control electrode 113 and thecathode 115 of each of the thyratron discharge devices 103 and 111. Thefirst 103 and second 111 inversely connected thyratron tubes areconnected together in inverse parallel relation and the parallelcombination is connected in series with the primary winding 33 of thehigh tension transformer 31 across suitable taps 8 and 9 on theautotransformer voltage supply source 7. The first thyratron tube 103 iscyclically controlled by an alternating current voltage applied to itscontrol electrode 165 by a first grid control secondary winding of asignal input coupling transformer 95. The second thyratron is similarlycontrolled by a voltage applied to its grid 113 from a second secondarywinding 9'9 of the signal input coupling transformer 95. The biasvoltage supplies 123 and 125, connected in series with the signal inputsecondary windings 99 and 100 are effective to maintain the respectivethyratron tubes nonconductive so long as no alternating current voltageis applied to the grids and 113 from the input signal couplingtransformer 95. The bias voltage supplies 123 and 125 shown in Fig. 2 asbatteries, may of course comprise a more complex DC. bias voltage supplymeans such as the type shown in the aforementioned US. Patent 2,785,343.By applying a control voltage from the coupling transformer secondarywinding 100 to the control electrodes 1&5 and 113 of the thyratrondischarge devices 103 and 111, they are caused to conduct either duringthe entire period in which their anodes 109 and 117 are positive withrespect to their cathodes 107 and 115, or by shifting the phase of thevoltage app-lied to the transformer 95, the thyratron discharge devices103 and 111 may be caused to conduct for any selected lesser portion ofthe period during which their anodes 109 and 117 are positive withrespect to their respective cathodes.

In Fig. 2 the X-ray tube voltage control brightness stabilizer circuit71 is shown as including a phase shift circuit 89' which comprisesalternating current windings 85 and 86 of a saturable reactor 81, thecenter-tapped secondary 92 of the contactor start transformer 91, and aphase shift resistor 93 connected in series relationship in a closedloop circuit. The two alternating current windings 85 and 86 of thesaturable reactor 81 are connected in opposing relationship in a mannerwell known in the art so that no alternating current voltage is coupledfrom the two secondary windings 85 and 86 into the D.C. control Winding83 of the saturable reactor 81. The primary winding 97 of the controlsignal coupling transformer 95 is connected across the phase shiftingnetwork 89' with one end of the primary winding 97 being connected tothe center tap of the secondary winding 92 and with the other end of theprimary winding 97 being connected to the closed loop circuit at theconnection between the phase shifting resistor 93 and the alternatingcurrent winding 85 of the saturable reactor 81.

An alternating current control signal which is applied to the contactorstart transformer 91 from the contactor start-stop circuit 87 is coupledthrough the phase shifting network 89 to the primary 97 of the controlsignal coupling transformer. Current flow in primary 97 inducescorresponding voltages in secondary windings 99 and 100 and saidvoltages are applied in opposing phase relationship to the respectivegrids 1G5 and 113 of the first and second thyratron tubes 103 and 111 inthe electronic contactor. By varying the impedance of the alternatingcurrent windings S5, 86 of the saturable reactor 81, it is possible tovary the phase relationship of the voltage applied to the controlelectrodes 105 and 113 of the thyratrons. The precise manner in whichthe phase shift network 89 operates to control the conductivity of thecontactor will be set forth in further detail hereafter.

The X-ray tube voltage control brightness stabilizer circuit 71 furthercomprises an electron discharge device 73 having a control electrode orgrid 75, a screen grid 76, a cathode 74 and an anode 77. A second outputsignal 55 from the brightness preamplifier circuit 53 is connected tothe grid 75 of the discharge device so as to apply a direct currentvoltage component corresponding to the brightness of the visible imagebetween the control electrode 75 and the cathode 74. The anode 77 of thedischarge device 73 is connected to a direct current voltage supplysource 82 through the D.C. control winding 83 of the saturable reactor81. The screen grid 76 of the discharge device is connected to the samedirect current voltage supply source 82 through a voltage droppingresistor 79. The cathode 74 of the discharge device '73 is connected tothe negative side of the direct current voltage supply source 82 througha cathode biasing resistor 80 and the negative side of the directcurrent voltage supply source 82 is further connected to the common sideof the brightness signal preamplifier second output circuit 55.

When an incremental change occurs in the brightness of the visible imageappearing at the fluorescent screen member 47, the photoelectric means49 transmits a component of D.C. signal current to the brightness signalpreamplifier circuit 53. The brightness signal preamplifier circuit 53is responsive to that change in brightness signal current to cause theimposition of a voltage component upon the grid of the discharge device'73 and to thereby cause a proportional change in the anode currentflowing through the discharge device 73 and through the D.C. controlwinding 83 of the saturable reactor 81. The saturable reactor thusconstitutes a variable impedance device which responds to the componentof D.C. current imposed upon its D.C. control winding 83. Upon anincrease in the current through the D.C. control winding 83 thesaturation of the reactor 81 increases, thereby causing a decrease inthe impedance of the alternating current windings 85 and 86.

When a reactor, such as the alternating current windings 85 and 86 ofthe saturable reactor, is connected across an A.C. voltage source, suchas the center-tapped secondary winding 92, the current in that reactorwill lag the applied voltage by an angle approaching 90 electricaldegrees. In contrast, if a resistor, such as the phase shifting resistor93, were connected directly across the A.C. voltage source, the resistorwould pass current in phase with the applied votlage. When the phaseshifting resistor 93 and the saturable reactor alternating currentwindings 85 and 86 are connected in series across an alternating currentvoltage source such as secondary winding 92 in Fig. 2, the samealternating current flows through both the resistor 93 and thealternating current windings 85 and 86. The alternating current voltagedrop across the resistor 93 lags approximately 90 electrical degreesbehind the voltage drop across the reactor 81, with the voltage drop ofthe resistor and the voltage drop of the reactor being vectoriallyadditive to equal the A.C. voltage applied by the secondary winding 92of the contactor start transformer 91.

Figs. 5 and 6 are vector diagrams illustrating, respectively, the phaserelationship of the various voltages in the phase shifting network forthe unsaturated and for the saturated condition of the saturable reactormember 81. In Fig. 5 is shown the phase relationship of the variousvoltages for the condition in which the reactor member 81 is relativelyunsaturated and has a relatively high impedance. The vector ABrepresents the alternating current voltage appearing across one section920 of the secondary winding 92. The vector BC represents thealternating current voltage provided by the second winding section 92bof secondary winding 92. The vector AD represents the A.C. voltageappearing across the phase shifting resistor 93 and the vector DCrepresents the voltage appearing across the alternating current windings85 and 86 of the variable impedance member 81. From the foregoing andfrom Fig. 5, it may be seen that the alternating current voltage appliedto the rimary 97 of the signal coupling transformer is represented bythe vector BD, and is equal to the vector sum of the voltages appearingacross winding section 92b and across the A.C. windings 85 and 86 of thesaturable reactance impedance member 81. It is to be noted that when theimpedance of the alternating current windings 85 and 86 of the saturablereactor is near a maximum, the vector DC representing the voltage acrossthat reactance 81 is much larger than the vector AD representing thevoltage across the phase shifting resistor 93. As a result, the vectorBD representing the voltage applied to the coupling transformer 95 lagsthe input voltage AB by approximately electrical degrees.

In Fig. 6 is shown the vector diagram of the various voltages appearingin the phase shifting network 89 in the condition wherein the reactormember 81 is highly saturated by an increased direct current flowingthrough the D.C. control winding 83 of the reactor member. The vector ABagain represents the voltage appearing across winding section 92a andthe vector BC again represents the voltage appearing across windingsection 92b. The vector AE represents the voltage appearing across thephase shifting resistor 93 and the vector EC represents the voltageappearing across the alternating current windings 85 and $6 of thesaturable reactor member 81. The

vector' sum of the voltage AE across the phase shifting resistor 93 andthe voltage EC across the saturable reactor is equal to the voltageapplied by secondary winding 92. The voltage applied to the primarywinding 97 of the coupling transformer 95 is now represented by thevector BE. The vector EC is now much shorter than the vector AE becausethe impedance of the alternating current windings 35 and 86 hasdecreased and is now smaller than the impedance of the phase shiftingresistor 93. The vector BE representing the votlage applied to theprimary winding 97 of the coupling transformer 95 now lags the vector BCby approximately 60 degrees. Thus, it is seen that by imposing acomponent of DC current upon the DC. control winding 83 of the saturablerector member 81, the phase of the voltage applied to the primarywinding 9'7 of the coupling transformer has been shifted throughapproximately 70 electrical degrees, and hence the alternating currentvoltages 7 applied to the respective grids 105 and 113 of the inverselyconnected thyratrons 103 and 111 has been shifted approximately 70degrees with respect to the alternating current voltages applied to theanodes 109 and 117 of the respective thyratrons. By proper choice ofcomponent values in the phase shifting network 89, it is possible tocause the voltages induced in secondary winding 99 and secondary winding100 to be so phased that the grid 105 of the thyratron discharge device103 will become positive with respect to the cathode 107 atapproximately the 90 point of the voltage wave applied to the anode 109.With that condition existing, the thyratron discharge devices 103 and111 will each begin to conduct at approximately the 90 point of theirrespective anode voltage waves and will continue to conduct so long asthe anode is positive with respect to the cathode, or for about 90electrical degrees from the 90 point to the 180 point of the anodevoltage wave.

It was previously considered important to make the firing point ofthyratron contactors occur as closely as possible to the zero point ofthe anode voltage wave in order to avoid the generation of transientvoltages in the high tension transformer of an X-ray machine. I havefound that in the use of an electronic contactor to control thecinefluorographic apparatus of the present invention the portion of thewave from zero to 90 electrical degrees applied to the primary of thehigh tension transformer contributes a negligible amount of energy tothevisible image appearing on the fluorescent screen member. I havefurther found that the formerly apprehended transient voltages do notoccur unless the X-ray tube current is reduced to an unusual minimum.Thus, it is advantageous to apply voltage to the primary of the hightension transformer 31 only during the period from 90 electrical degreesto 180 electrical degrees of the supply source wave, thereby reducingthe radiation impinging upon the patient and similarly reducing to aconsiderable extent the tendency of the X-ray tube 10 to overheat. Bycontrolling the DC. current applied to the DC. control winding 83 of thesaturable reactor 81 in the present apparatus, voltage is applied to theprimary 33 of the high tension transformer 31 during a maximum periodGH, as shown in Fig. 3, or during a minimum period KH, as shown in Fig.3. Thus, by automatic control of the saturable reactor 81 in response tochanges in brightness of the image appearing at the fluorescent screenmember 47, the X-ray tube voltage control brightness stabilizer circuit71 introduces a smaller or greater delay in the instant of firing of thethyratron contactor 101, thereby varying the voltage applied to theprimary 33 of the high tension transformer 31, and consequently varyingthe voltage applied to the X-ray tube 10 through r appearing across theX-ray tube 10 of the apparatus when,

the X-ray tube 10 is conducting approximately 20 milliamperes of anodecurrent. In Fig. 4, curve 150 represents the wave shape appearing at theoutput of a conventional full-wave rectifier, and is provided as areference wave shape. Curve 153 represents the voltage wave shapeappearing across the X-ray tube 10 when power is applied to transformer31 through a mechanical contactor. Curves 155 are oscillographicrepresentations of the voltage appearing across the X-ray tube 10 whenthe conduction of the thyratrons 103 and 111 is initiated at the pointof the thyratron tube anode voltage wave. The differential between waves153 and 155 is represented by 157 and results from the fixed anode tocathode voltage drop inherent in discharge devices 103 and 111.

If the phase shifting network 89 were arranged to vary the ignition timeof each thyratron across a time range FG, Fig. 3, from the 0 point tothe 90 point of the anode voltage wave, the peak voltage amplitudeapplied to the X'ray tube 10 would be varied through only a negligibleamount, less than the differential 157 shown in Fig. 4. In contrast, thestabilizer circuit 71 of this invention is preferably arranged to varythe ignition point of each thyratron 103 and 111 across a range GK fromapproximately the 90 point to approximately the point of its respectiveanode to cathode voltage wave. By providing that unusual range GK ofignition point control, the voltage applied to the X-ray tube 10 iscontrolled from a maximum as shown by curve to a minimum voltage whichresults from conduction period KH. Thus it is seen that the particularrange GK of ignition point control provides a maximum variation in thevoltage 155 applied to the X-ray tube 10 in response to a smallervariation in input signal than would otherwise be required. A givenincremental change in brightness of the image at screen member 47 is,therefore, accompanied by a larger change in X-ray tube voltage thanwould be the case if the ignition point were shifted within the rangeFG.

During a typical medical examination the body tissue and internal organsthat are being scanned by the image intensifier 43 may have widelyvariable absorption characteristics. In addition, barium sulphate, whichis often ingested by a patient for the purpose of gastro-intestinalexaminations is so X-ray opaque that various portions of the areasscanned may be almost entirely opaque to the X-ray beam. Under suchconditions the visible image at the fluorescent screen member 47 will besubject to sudden changes from low brightness to high brightness as theimage intensifier 43 and the X-ray tube 10 are moved with respect to thepatient 57. Under these conditions of rapidly and erratically changingimage brightness, any manual system of brightness control or filmdensity control would be clearly impractical. Likewise, the manualcontrol of voltage applied to the X-ray tube 10 alone would be helpfulbut not entirely adequate for maintaining optimum brightness and optimumcontrast. The control of X-ray tube anode current as by means of acurrent control brightness stabilzer circuit 132 alone would similarlybe inadequate to maintain optimum image brightness and optimum imagecontrast.

In the present apparatus, as the absorption characteristics of theobject scanned suddenly change from a minimum absorption to a maximumabsorption, the photosensitive member 49 will instantaneously anddynamically detect incremental changes in image brightness and willimpose a first signal voltage component 54! on the current controlbrightness stabilizer circuit 132 and a second signal voltage component55 on the X-ray tube voltage control brightness stabilizer circuit 71.The current control brightness stabilizer circuit 132 will increase theelectron emission of the X-ray tube filament 12 to thereby increase theintensity of the X-ray beam with an accompanying stabilization of thebrightness of the image at the fluorescent screen member 47.Simultaneously, the X-ray tube voltage stabilizer circuit 71 will shiftthe 11 phase of the alternating current control voltages applied to thecontrol grid 105 of the first thyratron tube 103 and the control grid113 of the second thyratron tube 111 so that the thyratron tubes willconduct during a greater portion of the applied anode voltage wave andwill thereby impress a higher energizing voltage on the primary 33 ofthe high tension transformer 31 during a greater portion of the cyclicalperiod of energization of the X-ray tube with an accompanying increasein the voltage applied to the X-ray tube 10.

When a relatively thin or relatively ray transparent portion of theobject scanned is interposed between the Xray tube 10 and the imageintensifier 43, the X-ray tube voltage brightness stabilizer circuit 71will automatically adjust the phase of the control voltage applied tothe thyratron grids 105 and 113. The said control voltages areimmediately caused to lag the alternating current voltage applied to thethyratron anodes 10s and 11.7 by approximately 150, thereby permittingthe thyratrons to conduct only during approximately the last 30electrical degrees of each successive half cycle of applied anodevoltage. The voltage applied to the X-ray tube anode ill will be lessthan one half of the maximum voltage which would be applied to the X-raytube anode if the thyratrons were allowed to conduct during the whole ofeach successive half cycle.

Thus, it is seen that the apparatus, including the X-ray generator, theimage intensifier tube 43, the photoresponsive means 49, the brightnesspreamplifier circuit 53, and the current and voltage brightnessstabilizer circiuts 132 and 71, is operative to simultaneously regulateboth the anode current conducted by the X-ray tube 10 and the anodevoltage applied to the X-ray tube to cooperatively stabilize thebrightness of the light image appearing at the fluorescent screen member47 in response to changes in the opacity of the object portion scannedby the X-ray beam.

A principal beneficial result obtained by the brightness stabilizationsystem is to maintain the visible image at the fluorescent screen member47 substantially constant so as to facilitate undisturbed viewing by thediagnostician and to maintain the density of films exposed in the motionpicture camera 59 substantially constant, thereby avoiding underexposedor overexposed film frames. A further important result realized by thestabilization apparatus is that the integral of the X-radiationimpinging upon the patient over any selected period of time isdynamically maintained at the absolute minimum commensurate withadequate photographic results. Thus it is possible to cinefluorograph asingle patient for longer periods of time to obtain longer sequences ofmotion picture than would be possible with any other known X-rayapparatus.

By proper selection of component values, the electronic contactor 101 issmoothly controlled to initiate conduction at points ranging fromapproximately the 90 point of each half cycle. The fractional portion ofeach half cycle during which the thyratrons 103 and 111 conduct isdependent on the brightness of the image at the fluorescent screen 47and is inversely responsive to incremental changes in the brightness ofthe visible image. Thus, the peak kilovoltage applied to the X-ray tube10 by means of the high tension rectifier unit 29 is varied in responseto changes in brightness at the fluorescent screen member 47 so thatlight intensity at the camera focal plane is maintained substantiallyconstant at a brightness level commensurate with optimum photographicefficiency.

As indicated by Figs. 3 and 4, it has been found that the voltagedeveloped across the Xray tube by the high voltage circuit is not adirect function of the R.M.S. voltage or the average voltage applied tothe primary winding 33 of the high tension transformer 31. Rather, thepeak kilovoltage applied to the X-ray tube 10 is dependent on the peakvoltage applied to the primary winding 33. Thus, controlling theelectronic contactor 101 so as to initiate conduction at differentpoints between the beginning and the points of each half cycle of thevoltage source wave would not have an appreciable effect on the peakvoltage applied to the transformer primary winding 33 and hence thekilovoltage applied to the X-ray tube 10 would not be satisfactorilyresponsive to phase shifting of the ignition point of the thyratrons 103and 111. In contrast, the voltage control brightness stabilizer circuitof my invention controls the electronic contactor 101 so as to causeconduction of the respective thyratron tubes at phase angles between the90 point of each half cycle and the point of each half cycle of thevoltage source wave form, thereby providing smooth continuousvariability of the X-ray tube anode to cathode potential in response tochanges in the brightness of the image at the fluorescent screen member47.

The light responsive member .9 or photoelectric means in a preferredembodiment of the invention comprises a photomultiplier tube having aplurality of dynodes, a cathode and an anode, and being responsive tovisible light such as that emanating from the fluorescent screen member4'7 to produce a direct current electrical signal which is proportionalto the brightness of the visible light image. The phototube power supply51 for the photomultiplier tube 47 may be any conventional source ofregulated high voltage direct current power. Such regulated voltagesupply sources are well known in the art. The image tube power supply 45is a DC. voltage source capable of energizing the image intensifier tube43 at a voltage of about 30,000 volts and capable of delivering a loadcurrent of about 2 milliamperes. Any of various well-known DC. powersupplies meeting the stated specifications may be used to supply powerto the image intensifier tube 43.

Although we have shown and described certain specific embodiments of thepresent invention, it should be apparent to those skilled in the artthat the invention is not limited to the specific embodiments described,but that many modifications thereof may be made. For example, the imageintensifier tube may not be desired and may not be necessary in aspecific embodiment, and instead of the X-ray responsive visible imageproducing member 47 may include an X-ray sensitive phosphor or likematerial which is directly responsive to X-rays from the X-ray tube 10to produce a visible light image.

I claim as my invention:

1. In X-ray apparatus including an X-ray tube having an anode and afilament and operable to project an X-ray beam through an object, thecombination of a fluorescent member operable to produce a visible image,photoelectric means associated with said member and responsive to thebrightness of said visible image, a source of electrical energy forheating the filament of said X-ray tube, an excitation circuit forsupplying current to the anode of said X-ray tube, said circuitincluding a contactor connected to control excitation of said X-raytube, a first image brightness stabilizer circuit connected between saidphotoelectric means and said contactor, a second image brightnessstabilizer circuit connected between said source of heating energy andsaid filament, with both said stabilizer circuits being responsive tosaid photoelectric means to maintain the brightness of said imagesubstantially constant.

2. In an X-ray apparatus including an X-ray tube having a filament to beheated and further including a fluorescent member to produce a visibleimage, the combination of an excitation circuit for said X-ray tubeincluding a high tension transformer and an electronic contactorconnected between said transformer and a source of supply voltage, aphase shift circuit connected to said contactor to control the cyclicaltime period of conduction thereof, said phase shift circuit including avariable impedance member responsive to imposition of a control voltagecomponent thereupon, a source of electrical energy for heating thefilament of said X-ray tube, inductive means connected between saidfilament and said source of heating energy and operable upon theimposition of a control current thereupon to control the flow of heatingcurrent to said filament, photoelectric means associated with saidfluorescent member and operative to produce an electrical output signalproportional to the brightness of said image, and circuit meansconnected to said phase shift circuit to impose a control voltagecomponent on said variable impedance in response to a change in saidelectrical output signal, said circuit means being also connected tosaid inductive means and operable in response to a change in saidelectrical output signal to cause the imposition of a control currentcomponent upon said inductive means.

3. In an X-ray apparatus, an X-ray tube having an anode and having afilament to be heated and operable to project an X-ray beam through anobject, a fluorescent member operable to produce a visible image of saidobject, photoelectric means associated with said fluorescent means andoperable to provide an electrical current proportional to the brightnessof said visible image, a source of electrical energy for heating thefilament of said X-ray tube, inductive means connected with said sourceof heating energy to control the flow of heating current to saidfilament, an excitation circuit for said X-ray tube including a hightension transformer having its primary winding connected through anelectronic contactor to a source of alternating current supply voltageand having its secondary connected to supply current to said X-ray tubeanode, first circuit means responsively associated with saidphotoelectric means and connected to said contactor to cause a variationin cyclical time period of conductivity of said contactor, and secondcircuit means responsively associated with said photoelectric means andconnected to said inductive means to cause the imposition of a controlcurrent component upon said inductive means accompanied by a variationin the heating current supplied to the filament of said X-ray tube, withboth said variation in heating current and said variation in cyclicaltime period being in inverse relation to variations in brightness ofsaid image whereby said brightness is maintained substantially constantregardless of variations in the density of said object.

4. In X-ray apparatus including an X-ray tube provided with a filamentto be heated and a fluorescent member for producing a visible image, thecombination of a voltage supply for said X-ray tube including a hightension transformer having its secondary winding connected in circuitwith said X-ray tube for supplying unidirectional current thereto andhaving its primary winding connected through an electronic contactorincluding a pair of inverse-parallel connected discharge devices to asource of alternating current supply voltage, an image brightnessresponsive means associated with said fluorescent member for Producing asignal voltage proportional to the brightness of said visible image, afirst image brightness stabilizer circuit including a saturable reactoroperatively connected with said X-ray tube filament and with a source offilament heating current and operable upon the imposition of a directcurrent component thereon to control the flow of heating current to thecathode of said X-ray tube, a second image brightness stabilizer circuitincluding a phase shifting network connected to said pair ofinverse-parallel connected discharge devices, with said secondstabilizer circuit being operable upon the imposition of a controlsignal thereupon, to control the cyclical time period of conduction ofsaid discharge devices, and circuit means connected between each of saidfirst and second image brightness stabilizer circuits and said imagebrightness responsive means to cause the imposition of control signalcurrent components upon said first and second stabilizer circuits inresponse to said signal voltage accompanied by a variation in theheating current supplied to the filament of said Xray tube and furtheraccompanied by a variation in cyclical time period of conduction of saiddischarge devices, said variations being inversely responsive tovariations in the brightness of said visible image, whereby thebrightness of said visible image is maintained substantially constant.

5. In X-ray apparatus including an X-ray generator and a fluorescentmember for producing a visible image, the combination of a photoelectricmeans associated with said fluorescent member and responsive to thebrightness of said image, an electronic contactor, a voltage supplycircuit connected through said electronic contactor to said X-raygenerator, and an image brightness stabilizer circuit connected betweensaid photoelectric member and said electronic contactor to control thecyclical time period of conduction thereof.

6. In X-ray apparatus including an X-ray generator and a fluorescentmember for producing a visible image, the combination of a photoelectricmember associated with said fluorescent member and responsive to thebrightness of said image, an electronic contactor, a voltage supplycircuit connected through said electronic contactor to said X-raygenerator, and an image brightness stabilizer circuit including a phaseshift network connected between said photoelectric member and saidelectronic contactor and operative to control the conductivity of saidcontactor in response to the brightness of said image.

7. ,In X-ray apparatus including an X-ray generator and a fluorescentmember for producing a visible image, the combination of a photoelectricmeans associated with said fluorescent member and responsive to thebrightness of said image, an electronic contactor, voltage supply meansconnected through said electronic contactor to said X-ray generator, andan image brightness stabilizer circuit connected between saidphotoelectric member and said electronic contactor, with said stabilizercircuit being connected so that -a variation in the brightness of saidimage causes the imposition of a voltage component upon said contactoraccompanied by a variation in the period of conductivity of saidcontactor inversely to the said variation in the brightness of saidimage.

8, In an X-ray apparatus including an X-ray generator, afluorescentmember to produce a visible image, and a photosensitivedevice having an output signal proportional to the brightness of saidimage, the combination of an electronic contactor connected so as toenergize said X-ray generator, a phase shift circuit connected to saidcontactor to control the period of conductivity thereof, said phaseshift circuit including a saturable reactor having a direct currentcontrol winding and means for passing a current proportional to saidoutput signal through said control winding.

9, In combination, an X-ray tube, an energizing circuit for successivelyenergizing said X-ray tube, an image intensifier embodying an electronimage of an object irradiated by said source and operative to provide avisible light image of said object, a light responsive member associatedwith said image intensifier and having an output voltage proportional tothe brightness of said image, photographic apparatus for cyclicallyrecording successive latent images of said light image, and an imagebrightness stabilizer circuit connected between said lightresponsivemember and said energizing circuit, said stabilizer circuit beingoperative to variably control the duration and intensity of each periodof energization of said X-ray tube by said energizing circuit, wherebythe density of said latent images are maintained substantially constant.

10. In X-ray apparatus including an X-ray generator and a commercialsource of alternating current voltage for energizing said generator, thecombination of a fluorescent image-forming member, a photoelectricmember associated with said image-forming member, an electroniccontactor including a pair of inverse-parallel connected unilaterallyconductive devices connected between said source and said generator, anda brightness stabilizer circuit including a phase-shifting network, withsaid confltactor being connected .to said phase-shifting network to beresponsive thereto and with said stabilizer circuit being connected tosaid photoelectric member to change the average conductivity of saidcontactor in inverse response to changes in brightness of said image.

11. In X-ray apparatus including a fluorescent member operable toproduce a visible image, an X-ray generator for projecting an X-ray beamthrough an object to said fluorescent member and further including anelectronic contactor for energizing said X-ray generator, thecombination of a light responsive member positioned relative to saidfluorescent member to be responsive to the brightness of said visibleimage and an image brightness stabilizer circuit connected between saidcontactor and said light-responsive member, with said circuit includinga phase-shifting network connected to a control element of saidcontactor and being operative to permit conduction by said contactorduring less than 90 electrical degrees of each successive half cycle ofan applied A.C. voltage wave.

12. An X-ray generator for projecting an X-ray beam through an object, afluorescent member operable to intercept said beam and to produce avisible image, a photosensitive member having an electrical outputsignal proportional to the brightness of said image, an electroniccontactor for said generator including a pair of inverseparallelconnected discharge devices each having a control electrode, and animage brightness stabilizer circuit connected between saidphotosensitive member and at least one of said control electrodes tovary the cyclic period of conductivity of said contactor in response tothe brightness of said visible image.

13. The apparatus of claim 12 wherein said stabilizer circuit comprisesa phase-shifting circuit, an alternating current voltage supply source,and a transformer having a primary connected in series with saidphase-shifting circuit and said A.C. voltage supply source, saidtransformer having a secondary winding connected in circuit with thecontrol electrode of one of said discharge devices.

14. In X-ray apparatus including an X-ray tube and a fluorescent screenfor producing a visible image, the combination of a voltage supplycircuit for said X-ray tube including a high tension transformer havingits secondary winding connected through a rectifying arrangement to saidX-ray tube and having its primary winding connected through anelectronic contactor to an alternating current supply source, alight-responsive member positioned relative to said fluorescent screento be responsive to the brightness of said image and having anelectrical output signal proportional to said brightness, aphaseshifting circuit including a variable impedance device associatedwith said electronic contactor and operable upon the imposition of acontrol signal current component thereupon to change the cyclical periodof conductivity of said contactor, and means connected to said lightresponsive member and responsive to variations in said electrical outputsignal to cause the imposition of a current component upon saidimpedance device accompanied by a variation in the cyclical period ofconductivity of said contactor.

15. In X-ray apparatus including an X-ray tube and a fluorescent screenfor producing a visible image, the combination of a voltage supplycircuit for said X-ray tube including a high tension transformer havingits secondary winding connected through a rectifying arrangement to saidX-ray tube and having its primary winding connected through anelectronic contactor to an alternating current supply source, with saidcontactor having a cyclical period of conductivity of variable timeduration, a light responsive member positioned relative to saidfluorescent screen to be responsive to the brightness of said image andhaving an electrical output signal proportional to said brightness, aphase-shifting circuit including a variable impedance device associatedwith said electronic contactor and operable upon the imposition of acontrol signal current component thereupon to change the cyclical periodof conductivity of said contactor, and means connected to saidlight-responsive member and responsive to variations in said electricaloutput signal to cause the imposition of a current component upon saidimpedance device accompanied by a variation in the cyclical period ofconductivity of said contactor.

16. Cinefiuorographic X-ray apparatus comprising an X-ray tube having ananode, cathode and filament, X-rayresponsive means for producing aluminous image, motion picture camera means for recording on film saidluminous image, first circuit means for controlling supply of current tosaid filament, second circuit means for controlling the voltage appliedacross said anode and cathode, and means responsive to the degree ofbrightness of said luminous image for controlling the aforesaid firstand second circuit means to maintain said degree of brightnesssubstantially constant.

References fiited in the file of this patent UNITED STATES PATENTS2,217,939 Bischofi' et al Oct. 15, 1940 2,246,884 Johnson June 24, 19412,316,566 Constable et al. Apr. 13, 1943 2,503,075 Smith Apr. 4, 19502,514,935 Clapp July 11, 1950 2,537,914 Roop Ian. 9, 1951 2,584,007Fischer Jan. 29, 1952 2,752,509 Zavales June 26, 1956 2,785,343 Wrightet al. Mar. 12, 1957 2,804,550 Artzt Aug. 27, 1957 2,823,301 StevensFeb. 11, 1958 2,837,657 Craig et al June 3, 1958 2,913,582 Collins et alNov. 17, 1959

